This invention relates to an appliance configured in reverse pendulum in relation to gravity, stabilised by a gyroscope, such as a two-legged robot according to the application given chief consideration.
Mobile robots are of extremely different make-up depending upon their missions and the pathways along which they are likely to travel, but the choice of a good solution raises problems in crowded environments littered with obstacles or with difficult access since the robot must then be provided with equilibrium, agility, flexibility and stability related properties so that it can make its way between obstacles, by-pass them or climb over them. Therefore tracked robots, some with several successive caterpillar axles, have been proposed. In one appliance actually built, the front caterpillar axle was articulated to the remainder of the robot so that it could be raised obliquely and assume the incline of stairs to be mounted: the caterpillar tracks of the front axle gripped several front treads at the same time enabling stair mounting to be initiated. But the drawback of caterpillar vehicles is a relatively large requirement of ground space and difficulty in accurate turning.
Robots mounted on feet or legs have also been put forward. Widely varying designs exist both in respect of the number of feet or legs and in respect of their properties, in particular concerning moving or shape changing possibilities. One extreme construction is a one-legged jumping robot provided with a single foot; this foot is rigid but ends in a jack allowing its periodic extension and it is jointed to a robot body to which it must give support. Sudden extension of the jack throws the robot body in the air and the piloting system adjusts the direction of the foot when it is lifted off the ground in order to prepare the following jump and re-balance the robot or move it in the required direction. Produced prototypes show that this concept is perfectly feasible despite its lack of static stability. However robots are generally preferred which are equipped with a much higher number of feet and six-footed robots have in particular met with real popularity. The six feet are distributed into two groups of three which alternately carry out the same work: one of the groups of feet rests on the ground and maintains the robot body in equilibrium while the other group is lifted and moved forward before being lowered to provide new support to the robot ahead of the previous support, which enables the robot body to be moved forward when the first group of feet is lifted. This is a very stable construction since the feet of each of the groups are arranged in a triangular base within which the centre of gravity of the robot is always contained. But this stable equilibrium is obtained at the price of the robot""s complexity, large space requirement and relatively considerable weight.
There is a temptation, however, to recall that artificial environments such as factories, in which numerous robots need to move around, were firstly designed for man, and to draw the conclusion that a robot imitating the form and walk of man as near as possible should give the best results by offering a satisfactory compromise between complex robots that are highly stable but voluminous and robots with a reduced number of feet whose equilibrium raises problems. Experience has shown that two-legged robots, made up of legs articulated independently from the robot body and fitted with a knee joint for alternate flexing and extension to imitate man""s walk, require less space and can be of use in difficult, complicated situations by overcoming varied obstacles. Strict co-ordination however of the different motors controlling the articulations is required to maintain equilibrium, and imitation -of man""s walk is less easy than may be thought.
The purpose of the invention is therefore to bring radical improvement to the stability of appliances having relatively unstable equilibrium, for example those configured in reverse pendulum such as one-legged, two-legged or even three-legged robots, since at certain times during their movement they are only supported by two legs, by equipping them with a gyroscopic rotor wheel located in an upper body supported by the leg or legs. The gyroscopic rotor wheel forms a xe2x80x9cinertial fulcrum pointxe2x80x9d which, for an appliance whose static equilibrium is not assured, fulfils the same role as a balancing pole for a tightrope walker; the invention also comprises the automatism parts which make use of this fulcrum point (sensors or detectors, command system, actuators positioned between the balancing pole and the tightrope walker to use the former image) in order to balance the appliance in any position for a certain period of time. In other words, the invention also enables stability to be imparted to the reverse pendulum appliance at any time, even if the supporting leg is strongly inclined, provided however that certain operating conditions are met.
This rotor wheel, intended to assure equilibrium, is to be distinguished from the gyrometer of the robot in the article published by Matsumoto et al xe2x80x9cA four-wheeled robot to pass over steps by changing running control modesxe2x80x9d (IEEE International Conference, May 21, 1995, p. 1700 to 1706) which only serves to measure its tilt when in dynamic equilibrium and in no way contributes towards this equilibrium.
The operating conditions of the rotor wheel are related to the orientation of its spin axis, either relative to gravity or relative to the mechanical suspension between the rotor wheel casing and the upper body (for a one-legged appliance) or the intermediate body (for an appliance with at least two legs). These vary continually taking into account that the spin axis of the rotor wheel drifts under the effect of precession. In particular, this drift limits the time interval in which it is possible to immobilise the appliance in a position in which its supporting leg is strongly inclined. It is possible to correct this effect by voluntary shifting of the whole appliance into a symmetrical configuration (or a series of configurations whose resultant is symmetrical) relative to the equilibrium configuration of the reverse pendulum, either by a strong tilt maintained for a short period of time, or by a less inclined tilt maintained for a longer time interval. It can therefore be seen that the invention is particularly well adapted to the stabilisation of a walking two-legged robot which naturally alternates tilting.
The gyroscopic rotor wheel is placed in a casing, itself connected to the upper body of the appliance by a mechanical suspension which allows rotating movements about two nonparallel axes. This suspension with two nonparallel axes is equipped with actuators able at any time to exert, between the rotor wheel casing and the upper body of the appliance, a stabilising couple which opposes the off-balance effect produced by gravity on the appliance.
The command system adapted to the invention is able to measure the tilt effect produced by gravity on the appliance, to give a command for opposing action to the activators appropriate to achieve perfect balance of the appliance, and to maintain this appliance within its operating conditions. It is also able to co-operate with another command system, such as a system intended to command forward movement of the robot, the latter system therefore being released of the function consisting of seeking and maintaining equilibrium.
This task separation between the two command systems, one managing the robot""s equilibrium and the other its forward movement, is an important advantage of the invention which makes co-operation between the systems easy by doing away with the need for their coordination or strict synchronisation. It sets itself well apart from the invention in the article xe2x80x9cThe walking gyroxe2x80x9d (Robotics Age, vol. 7, No. 1, January 1985, pages 7 to 10, Peterborough, NH, USA) in which a gyroscopic rotor wheel undergoes tilting whose effect is to incline a rod in the form of a balancing pole at whose ends are fixed the feet of a two-legged robot: the rotor wheel serves to lift the feet alternately without referring to any other robot functions (such as equilibrium or walking).
To resume, the invention concerns an appliance made up of at least one supporting leg and an upper body connected to the supporting leg, and configured in reverse pendulum relative to gravity, characterised in that the upper body comprises a gyroscopic rotor wheel rotating around a rotor axle and housed in a casing, the casing being connected to the upper body by a mechanical connection which permits rotational movements about two non-parallel axes, in that the appliance comprises sensors with which the gravity-produced off-balance effect can be measured (moment of tilt), means able to equilibrate the appliance by exerting opposite forces to the imbalance (opposing moment) which use the support of the gyroscopic rotor wheel by means of actuators, and in that it comprises a command system able to take advantage of the actuators and sensors of the apparatus to assure its equilibrium at all times and even to co-operate with other command systems intended in particular to control locomotion or pathway. One preferred embodiment consists of making the mechanical connection adjustable between the rotor wheel and the upper body by means of a Cardan suspension. In this case, the casing containing the rotor wheel is suspended from an inner suspension ring by an inner rotating suspension axle perpendicular to the rotation axle of the rotor wheel, and this inner ring is itself suspended from an outer suspension ring by an outer rotating suspension axle perpendicular to the inner rotating suspension axle. The outer suspension ring is integral with the upper body of the appliance to be balanced. The inner and outer suspension axes therefore form the effective mechanical axles along which suspension is built.
The invention may, advantageously, comprise several legs and form a walking two-legged robot which naturally alternates tilting. According to one particular embodiment, it comprises two supporting legs jointed with the upper body, each made up of two sections jointed together. Each of these sections may comprise a foot, connected to the lower section by a joint having a vertical axis, fitted with a motor, which allows changes of direction when walking. Said robot is able to be in equilibrium at all times, even when its centre of gravity is off-centre in relation to its base, such as for example during the phase of walking when it is strongly inclined and on the point of placing its second foot on the ground.
Advantageously, the off-balance effect due to gravity on the appliance may be measured by two tiltmeters or two sensors of angular velocity placed along orthogonal axes, either on the leg for a one-legged robot or on one connecting section for a two-legged robot.
For walking robots, the command system may make use of the alternate moments of tilt by seeking to make their average over a time period virtually zero or, which amounts to the same thing, to make the average of compensating opposing moments virtually zero.
The invention may advantageously comprise means with which it is possible to measure the orientation of the spin axis of the rotor wheel, in order to monitor the operating conditions of the appliance taking into account that the spin axis of the rotor wheel drifts under the effect of precession. One simple means of measuring this orientation consists of placing angle position sensors on the mechanical suspension axles and to connect these to a specific part of the command system.